1. Field of the Invention
The present invention relates to a voltage non-linear resistor comprising, as its main ingredient, zinc oxides, and more particularly a voltage non-linear resistor which is excellent in lightning discharge current withstanding capability and exhibits a strong coherency between its disclike resistance element and insulating covering layer, and also to a process for manufacturing the same.
2. Description of the Prior Art
As a manufacturing process of voltage non-linear resistors having been heretofore extensively utilized in voltage stabilizing devices, surge absorbers, arrestors, etc. which have characteristics of acting as an insulator usually but as a conductor when an overcurrent flows, is widely known, for example, a process for manufacturing a voltage non-linear resistor by forming a disclike body from a starting material mixture consisting of 0.1-3.0% Bi.sub.2 O.sub.3, 0.1-3.0% Co.sub.2 O.sub.3, 0.1-3.0% MnO.sub.2, 0.1-3.0% Sb.sub.2 O.sub.3, 0.05-1.5% Cr.sub.2 O.sub.3, 0.1-3.0% NiO, 0.1-10.0% SiO.sub.2, 0.0005-0.025% Al.sub.2 O.sub.3, 0.005-0.3% B.sub.2 O.sub.3 and the remainder of ZnO (% stands for mole %) and then sintering the formed body.
Further, when voltage non-linear resistors obtained by the above-described process are used under high humid conditions, resistivity at the peripheral side surface of the discal element decreases and, therefore, an improved process for manufacturing a voltage non-linear resistor, taking measures for humidity proof, by providing the peripheral side surface with a high resistance layer composed of an epoxy resin or the like has also been known.
Conventional voltage non-linear resistors manufactured by the above-mentioned processes have such a wide composition range of components and such a low cohering strength between the resistance element and the high resistance layers on its peripheral side surface that flashover of the element due to lightning discharge current, etc. has been unable to be effectively prevented. Further, since the voltage non-linear resistors manufactured by conventional processes are poor in uniformity at each part, a big current locally flows upon application of lightning discharge current, etc., which sometimes causes to destroy the resistors. Consequently, a voltage non-linear resistor satisfactory in lightning discharge current withstanding capability that is particularly important in protection of an electrical insulator, has not always been obtainable.